Abstract

Continuous observational monitoring of a study site in eastern Christchurch, New Zealand, following the 2010 Mw 7.1 Darfield earthquake has recorded ten distinct liquefaction episodes in the mainshock–aftershock sequence. Three nearby accelerometers allow calibration between the geological expressions of liquefaction and the intensity of earthquake-induced surface ground motion at the site. Sand blow formation was generated by Mw 5.2–7.1 earthquakes with Mw 7.5–normalized peak ground accelerations (PGA7.5) of ≥ 0.057 g (acceleration due to gravity). Silt drapes between successive sand blow deposits provide markers for delineating distinct liquefaction-inducing earthquakes in the geologic record. However, erosion quickly modifies the surface of sand blows into alluvial and aeolian forms that complicate geologic diagnosis. The two feeder-dike generations identified in subsurface investigations significantly underrepresent the number of liquefaction-inducing earthquakes due to extensive dike reactivation. New constitutive equations enable PGA7.5 variations to be estimated from the thickness and areal extent of sand blows.

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